After children are diagnosed with autism, both they and their younger siblings are less likely to receive all recommended vaccinations, according to new research.

The findings published Monday in JAMA Pediatrics suggest that concerns linger among some parents about whether immunizations cause autism, despite previously debunked claims.

The study compared vaccination rates among children with a diagnosed autism spectrum disorder and those without, as well as rates among both groups’ younger siblings. For kids not on the spectrum, 94 percent had received all vaccines recommended between ages 4 and 6. But for children with autism, only 82 percent had received all their shots.

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“You have about a 12 percent difference and that is very significant,” said lead author Ousseny Zerbo, a postdoctoral fellow with the Kaiser Permanente Northern California Division of Research. “When you are not fully vaccinated, you are at higher risk of vaccine preventable diseases.”

Vaccination rates were also lower among younger siblings of children with autism. For instance, for immunizations recommended in infancy, 73 percent were fully vaccinated compared to 85 percent of the younger siblings of children not on the spectrum.

Zerbo described the study as the largest of its kind. While researchers analyzed vaccination data, they did not explore the reasons why children were not fully vaccinated.

“We are following up on this study to try to understand what makes parents reluctant,” Zerbo said. “The study does not tell us why we are seeing this disparity.”

Dr. Carolyn Bridgemohan, co-director of the Autism Spectrum Center at Boston Children’s Hospital, said she hears from parents who have concerns about vaccines based on flawed research.

“That message got out there and perpetuated,” she said. “I think when parents look to either social media or the internet they may come up with a lot of information that is not validated but it may raise their fears.”

Bridgemohan, a developmental behavioral pediatrician, said it’s important for doctors to have nonjudgmental communication with parents while providing accurate information.

“Without that kind of trusting relationship, it’s really hard to dispel fears that a family might have,” Bridgemohan said. “We do know there are no studies that show an increased risk of autism from any of these vaccines.”

The study was funded by the Centers for Disease Control and Prevention and included roughly 3,700 children with autism spectrum disorder and 600,000 kids without. The children were from California, Colorado, Oregon, Washington state and Wisconsin.